The measuring electrode buffer for a pH electrode is typically which salt solution?

The measuring electrode buffer for a pH electrode is typically which salt solution?

• A. KCl
• B. NaCl
• C. Hepes
• D. Phosphate

Answer: (A)

The main idea is that the reference electrode in a pH probe needs a very stable, known chloride ion activity to keep its potential constant. This is achieved by filling the reference electrode with potassium chloride (KCl), usually at a saturated concentration. The KCl solution provides high ionic strength and a steady Cl− supply that maintains the Ag/AgCl reference reaction at a constant potential, minimizing drift when you measure pH. It also offers good conductivity and compatibility with the glass electrode. Hepes and phosphate are buffering agents used to stabilize pH in solutions, not filling solutions for the reference electrode. Sodium chloride could supply chloride, but saturated KCl is preferred because it better stabilizes the reference potential and reduces junction potential drift, making it the standard choice.

The main idea is that the reference electrode in a pH probe needs a very stable, known chloride ion activity to keep its potential constant. This is achieved by filling the reference electrode with potassium chloride (KCl), usually at a saturated concentration. The KCl solution provides high ionic strength and a steady Cl− supply that maintains the Ag/AgCl reference reaction at a constant potential, minimizing drift when you measure pH. It also offers good conductivity and compatibility with the glass electrode.

Hepes and phosphate are buffering agents used to stabilize pH in solutions, not filling solutions for the reference electrode. Sodium chloride could supply chloride, but saturated KCl is preferred because it better stabilizes the reference potential and reduces junction potential drift, making it the standard choice.